Metal gaskets are often used as seals between mating metal surfaces. One common application involves gasket placement between a head and an exhaust manifold of an internal combustion engine. Another application involves gasket placement between the exhaust manifold and an exhaust pipe flange. Gaskets in either location can be described as exhaust manifold gaskets. The gasket between the engine head and the exhaust manifold surrounds exhaust ports in the engine block to provide an exhaust seal. Similarly, the gasket between the exhaust manifold and the exhaust pipe flange surrounds the opening of the exhaust manifold to provide an exhaust seal. Both exhaust manifold gaskets prevent hot combustion products exiting the engine from escaping into the engine compartment of the vehicle.
Exhaust manifold gaskets are typically installed by aligning bolt holes or apertures in the gasket with corresponding holes in the exhaust manifold. The exhaust manifold and gasket are then aligned with corresponding threaded apertures in the cylinder head. A first bolt is then threaded into the engine cylinder head. Bolts are then passed through the remaining apertures. Some maneuvering of the manifold and gasket relative to the engine cylinder head may be required to align the holes therein with the corresponding threaded apertures of the engine cylinder head before the bolts can be inserted.
Similarly, the exhaust gasket between the manifold and the exhaust pipe flange are assembled with a bolt passing through the aperture of the exhaust manifold and a corresponding aperture of the gasket and threading into the exhaust pipe flange, a weld nut fixed to the flange, or a nut disposed beneath the flange, or stud and nut assembly.
There are several difficulties in such an assembly process. For example, the gasket may slip from its desired position, or drop off the end of the inserted bolt or stud altogether, before it can be fixed in place between the exhaust manifold and its mating surface. It would be highly desirable to have a gasket that will not fall off the threaded ends of the bolts after bolts have been passed through bolt holes in the gasket. Thus, an assembler could maintain the gasket in place relative to the manifold when mating the manifold to both the engine head and the exhaust pipe flange.
Several methods exist for capturing the threaded ends of screws, but none are well suited for use with exhaust manifold gaskets. One approach for retaining bolts is to provide a star shaped opening defining inwardly directed fingers in soft gasket material. Pushing a bolt through the gasket opening causes the fingers open outward in the direction of motion of the bolt, partially covering the bolt. The gasket material around the bolt is compressed when the gasket is subsequently clamped, with the material on the side of the bolt providing a seal around the bolt. Use of this configuration with a steel gasket would be problematic because the high bending strength of steel would resist insertion of the bolt and the resultant axially extending fingers would prevent the mating surfaces from being drawn together to form the desired seal.
Retention means in gaskets have also been employed to fix the gasket over locating pins as is done with head gaskets. An aperture in the gasket has radially extending fingers which engage the pin. As the gasket is pushed down over the pin, the fingers deflect upward, locking the gasket to the pins at the aperture. The fingers act as a unidirectional brake, resisting efforts to subsequently lift the gasket from the pin. One problem with this approach as applied to threaded fasteners is that with the fingers so engaging the fastener, the torque to turn the bolt would be undesirably increased. Another problem is that such a retention means may damage the threads of the fastener.
In short, there is no affirmative teaching in the prior art of how to retain a metal gasket on a threaded bolt passing through an exhaust manifold.